How was the study conducted?Thirty-three University of British Columbia undergrads watched videos of tennis players hitting a ball to either side of a tennis court. With some shots, participants heard a brief grunting sound when the player hit the ball. Study participants were asked to note the direction of each shot, but their ability to do so quickly and accurately decreased when the sound was heard. (Watch a female tennis player grunt during a match)

What conclusion did researchers reach?"The findings were unequivocal," says Scott Sinnett, the study's lead author. "When the video clips did have a grunt, the participants were not only slower to react but they had lower accuracy levels." Although the study has yet to be conducted on an actual tennis court, Sinnett and colleagues believe that, in real-world scenarios, a player's grunting similarly affects his or her opponent's shot perception and reaction time.

Is grunting in tennis really that big a deal?Many observers consider it a negative for both grunters' opponents and fans. Martina Navratilova has likened it to cheating. If a player grunts, explains Bill Babcock, the International Tennis Federation's Grand Slam director, "the noise extends into the hitting preparation time of her opponent, and that creates problems." Meanwhile, says Sue Barker, a tennis presenter for the BBC and a former French Open champion, "grunting spoils [fans'] enjoyment of a match... it’s unattractive; it’s distracting. I would like to see it ultimately done away with."

Who are some of professional tennis's most notorious grunters?Grunting is most common among the women. The loudest include Maria Sharapova, whose grunts have measured 101 decibels (a lion's roar is 110), along with Monica Seles and Serena Williams, whose grunts have measured 93.2 and 88.9 decibels, respectively. Portugal's Michelle Larcher de Brito drew complaints at the 2009 French Open for her uniquely high-pitched, prolonged wails. Among males, Rafael Nadal is often mentioned, and Andre Agassi was an early offender. At the 1988 U.S. Open, Ivan Lendl complained about Agassi's noise levels: "The noise threw my mental game," said Lendl, who still managed to beat Agassi.

Why do tennis players grunt anyway?"Players grunt because it helps them release energy and keep focused," says top tennis coach Nick Bollettieri, who, despite having worked with notables grunters like Agassi, Seles, and the Williams sisters, insists he does not encourage the practice. "It is something that they do naturally... [not] deliberately to hurt their opponents."

Are there any rules against grunting in professional tennis?As it stands now, an official can award a point against a grunting player if her noises are deemed to have hindered her opponent. The International Tennis Federation is currently considering a tougher "noise hindrance" ruling that could force an excessive grunter to forfeit an entire game or even the whole match.